Grog in clay for throwing

I usually throw cone 5 stoneware without grog. I have recently moved from Southern Africa back to USA and by mistake got some clay with fine grog. I am at a loss how to smooth it, as a damp sponge just brings up the grog. B.T.W. Is grog needed in clay for throwing? The only way I could solve the problem was to make a sieved slip from the clay body, or burnish. How to others deal with this?
Is there a rule of thumb about when grog is needed? I've read it's a must for tiles, but what else?

I 'm sure my question is very basic and dumb, but I learned to throw in sort of a vacuum being in Africa and all.........
Thanks!
Val

Grog is not necessary, although it does improve the workability of the clay, plus reduces shrinkage, cracking and warping. You can make just about anything with any clay body, but grog makes it more forgiving. I just bisque fired 28 inch tall porcelain vase with no problems.....

While it can improve the plastic throwing/forming qualities of some clays, and can help with potential drying issues by letting moisture more easily migrate through the walls, and even out/decrease shrinkage helping to prevent things like warping, grog is a double-edged sword.

The shrinking clay surrounding the already fired grog particles sets up a network of micro-cracks surrounding the grog pieces that form the basis for later failure under stress. This process starts in the wet to dry shrinkage, and continues in the dry to fired stage.

Hi guys, just a real newbie question on this issue- if you are making your own bisqued clay grog for a clay body, does the grog have to be made from the same body? For e.g. porcelain for porcelain, earthenware for earthenware?

Biglou, I have no idea at the moment how I'm going to make grog! It's been suggested that it would be possible to smash the bisqued clay up inside a heavy duty bag of some sort using a tenderiser or some type of hammer and then sieving, or grinding with a mortar & pestle (and then sieving). I'm not talking large quantities, just experimenting at this stage!

I have thrown a lot of different clays, some with and some without grog. I used to like the grog for tooth and strength when throwing larger, but have found over the years that most of the finer grogged or minimally grogged clays work just as well for me. Extremes don't do a whole lot, 50% grog as in Penn States raku clay during Don Tigney years was brutal-open sores all summer long. At the same time throwing a fast drying raku that had 35% perlite was skill taxing. Imagine stretching a belly wall out with that stuff in the clay! So now my clays are pretty smooth and plastic from SC.

Fine grog is good for you. Why even worry about it? How can this be a mistake? You used wrong "tool" to smooth the surface

If you get clay with >2 mm grog, this starts to be a tricky stuff to throw because it's really hard on your hands. Ever fallen down on coarse asphalt and got your palm all scraped?

...The shrinking clay surrounding the already fired grog particles sets up a network of micro-cracks surrounding the grog pieces that form the basis for later failure under stress. This process starts in the wet to dry shrinkage, and continues in the dry to fired stage.

best,

.................john

Hmm... this sounds interesting, especially the "continues in the dry to fired stage".Can you elaborate on this particular phenomena?

Fine grog is good for you. Why even worry about it? How can this be a mistake? You used wrong "tool" to smooth the surface If you get clay with >2 mm grog, this starts to be a tricky stuff to throw because it's really hard on your hands. Ever fallen down on coarse asphalt and got your palm all scraped?

...The shrinking clay surrounding the already fired grog particles sets up a network of micro-cracks surrounding the grog pieces that form the basis for later failure under stress. This process starts in the wet to dry shrinkage, and continues in the dry to fired stage.best,.................john

Hmm... this sounds interesting, especially the "continues in the dry to fired stage".Can you elaborate on this particular phenomena?

Here is a picture I'll let sensei John explain. (Plus not sure how to explain it). But there were cracks in bone dry stage and even bigger in, fired. I look to refire these .
A picture is worth a lot o words.
(3 day woodfire, self made clay, granite inclusions, aka chicken grit, first firing)

Biglou, I have no idea at the moment how I'm going to make grog! It's been suggested that it would be possible to smash the bisqued clay up inside a heavy duty bag of some sort using a tenderiser or some type of hammer and then sieving, or grinding with a mortar & pestle (and then sieving). I'm not talking large quantities, just experimenting at this stage!

Fine grog is good for you. Why even worry about it? How can this be a mistake? You used wrong "tool" to smooth the surface If you get clay with >2 mm grog, this starts to be a tricky stuff to throw because it's really hard on your hands. Ever fallen down on coarse asphalt and got your palm all scraped?

...The shrinking clay surrounding the already fired grog particles sets up a network of micro-cracks surrounding the grog pieces that form the basis for later failure under stress. This process starts in the wet to dry shrinkage, and continues in the dry to fired stage.best,.................john

Hmm... this sounds interesting, especially the "continues in the dry to fired stage".Can you elaborate on this particular phenomena?

Here is a picture I'll let sensei John explain. (Plus not sure how to explain it). But there were cracks in bone dry stage and even bigger in, fired. I look to refire these .A picture is worth a lot o words.(3 day woodfire, self made clay, granite inclusions, aka chicken grit, first firing)

If you got visible cracks at try stage, you will get bigger cracks after the firing. There is no magic involved in this, grog or no grog. This is how clay behaves.

What I was curious about, are those micro cracks, John was talking about. Maybe it's a question of definition? When most of the added water has evaporated, dry clay is one big pile of "micro cracks" As little as I understand, those "micro cracks" vanish in firing thanks to vitrification.

Biglou13, that little plate looks awesome. Refiring will ruin it for sure.